Protein tyrosine phosphatase (PTP) may play a key role in controlling cell growth and proliferation as well as possible in tumor suppression. Two different cDNAs encoding PTP have been isolated from mouse testis and T-cell cDNA libraries, and their nucleotide sequence determined. The expression of these PTP-1 and PTP-2 genes from different mouse tissues was investigated by Northern blot analysis. The PTP-1 gene was found to be abundant in testis as well as brain.